Laser machining apparatus with deformable mirror

ABSTRACT

In the present invention, a curvature variable reflector made from a material capable of elastically deforming in response to a fluid pressure is formed to a curved-face mirror by making use of a pressure by a fluid such as air so that a diameter of a laser beam coming into a converging optical member can be changed at a high speed step by step or smoothly. And by controlling the fluid pressure step by step or steplessly according to a type or thickness of a work, machining can always be performed with an appropriate laser beam diameter.

FIELD OF THE INVENTION

The present invention relates to a transfer technology for a laser beamin a laser machining apparatus, and more particularly to a controltechnology for a laser beam diameter.

BACKGROUND OF THE INVENTION

FIG. 8 is a cross-sectional view illustrating a conventional type ofcurvature variable reflecting curved-face mirror (a concave mirror), forinstance, disclosed in Japanese Patent Laid Open Publication No.159613/1986, and FIG. 9 is a perspective view thereof.

In the figure, designated at the reference numeral 1 is an air-tightvessel, at 2 a circular opening formed on the top edge thereof, at 3 adisk-shaped film with a peripheral section thereof fixed to the vessel1, and at 4 a sealed tight space defined by the film 3 and the vessel.

Also, at 5 is a pressure adjusting means for adjusting a pressure in thesealed space 4, which comprises an air path 6 provided in the vessel 1,a valve 7 for opening/closing the path, and a pump 8 for discharging theair in the space 4.

In the curvature variable reflecting curved-face mirror (a concavemirror) constructed as described above, when the valve 7 is opened andthe pump 8 is actuated, the air in the space 4 is discharged through theair path 6, so that the pressure inside of the vessel 1 becomes lowerthan that outside thereof. With this feature, a pressure difference isgenerated between the top and rear surfaces of the disk-shaped film 3,and for this reason this disk-shaped film 3 is deflected toward insidethereof.

Then the reflecting surface 3a which is an external surface of the filmformes a substantially rotative paraboloid. For this reason, if anelectromagnetic wave such as a light comes into this curved-face mirrorfrom the above direction, the electromagnetic wave is focused to almostone point by the reflecting surface 3a. Namely, the mirror can be usedas a concave mirror.

Then when a focus of the reflecting surface 3a reaches a prespecifiedposition, an air flow inside and outside of the vessel 1 can be stoppedby closing the valve 7, and a form of the disk-shaped film 3 can be keptconstant.

Also if it is arranged so that air can be supplied from outside into thespace 4 of the vessel 1 by the pump 8, the pressure in the vessel 1 canbe made higher than that outside thereof, so that the reflecting film 3acan be deflected toward outside thereof. For this reason, a convexmirror can be formed therein.

The curvature variable reflecting curved-face mirror based on theconventional technology is constructed as described above, and for thisreason it is required for the purpose to change the curvature to changethe pressure inside of the vessel 1 by actuating the pump 8, and acertain time is required until the curvature becomes as prespecified, sothat, for instance, in a light scan type of laser machining apparatus inwhich a machining head moves on an X-Y plane and executes machining, ina case where the curvature variable reflecting curved-face mirrordescribed above is used for reflecting a laser beam, it has beendifficult to keep constant a diameter of a laser beam coming into aconverging optical member by changing a diameter of laser beam at a highspeed in association with movement of the machining head.

SUMMARY OF THE INVENTION

It is an object of the present invention to obtain a laser machiningapparatus which can change a curvature of a laser beam reflecting memberat a high speed, and at the same time can freely control a curvaturethereof as required.

The laser machining apparatus according to the present inventioncomprises a laser beam reflecting member which elastically deformsaccording to a fluid pressure provided in a transfer path for the laserbeam, a reflecting member supporting section for supporting a peripheralsection of this laser beam reflecting member and also defining a spacein a side opposite to a laser beam reflecting surface together with thelaser beam reflecting member, a fluid supplying means for supplying afluid into the space defined by this reflecting member supportingsection, and a fluid discharging means for discharging a fluid from thespace defined by the reflecting member supporting section, and the spaceis sealed excluding a fluid feed path and a fluid discharge paththereof, a fluid path in which a fluid supplied into the space isdischarged to outside thereof is defined by contacting with a laser beamreflecting surface, and a fluid pressure required for the laser beamreflecting member to elastically deform is loaded to the laser beamreflecting surface.

Also the apparatus comprises a fluid pressure control means forcontinuously controlling a supplied fluid pressure, and a diameter of alaser beam coming into a converging optical member is continuouslycontrolled by continuously changing curvature of the laser beamreflecting member due to its elastic deformation.

Also after the fluid supplied to elastically deform the laser beamreflecting member is discharged from the fluid discharge means, thefluid is used for purging inside of the laser beam transfer path as apurge air by supplying it thereinto.

Also the apparatus comprises a means for controlling curvature of thelaser beam reflecting member so that, in a case where a light scan typeof laser machining in which a machining head moves on an X-Y plane andexecutes machining is used, a diameter of a laser beam coming into theconverging optical member mounted on the machining head will be keptconstant irrespective of a position of the machining head.

Also the apparatus comprises a means for controlling a basic body of themachining head or the converging optical member mounted on the machininghead to move in the Z-axial direction, so that a position of the minimumconverging spot diameter in the Z-axial direction will be kept constant.

Also a plurality of laser beam reflecting members which elasticallydeform due to a fluid pressure are provided in the laser beam transferpath, so that a variable range for a laser beam diameter can beexpanded.

Also a supplied fluid pressure is monitored when a pressure of a fluidsupplied into the space defined by the reflecting member supportingsection is being controlled, and alarm is generated or operation isstopped when a difference equal to or larger than a prespecified valueis generated between the monitored fluid pressure and an instructedpressure value.

Also optimal laser beam diameters are previously registered as machiningconditions and one of the laser beam diameter is selected according to aquality or a plate thickness of a work.

Other objects and features of this invention will become understood fromthe following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an optical path configuration, aholder construction, and a piping system of a laser machining apparatusaccording to Embodiment 1 of the present invention;

FIG. 2 is another block diagram showing configuration of an optical pathas well as a piping system of the laser machining apparatus according toEmbodiment 1 of the present invention;

FIG. 3 is a block diagram showing a piping system and its constructionin a case where air discharged from a holder for a curvature variablereflector of the laser machining apparatus according to Embodiment 1 ofthe present invention is used as purge air;

FIG. 4 is a block diagram showing a control circuit for keeping adiameter of the laser beam constant in a position of the machining lensof the laser machining apparatus according to Embodiment 1 of thepresent invention;

FIG. 5 is a block diagram showing a control circuit for moving amachining head in the Z-axial direction corresponding to a change of adistance from the machining lens to a minimum converging spot diameterof the laser machining apparatus according to Embodiment 1 of thepresent invention;

FIG. 6 is a block diagram showing an alarm circuit for an air pressuresupplied to the holder for curvature variable reflector of the lasermachining apparatus according to Embodiment 1 of the present invention;

FIG. 7 is a block diagram showing the holder construction and pipingsystem of the laser machining apparatus according to Embodiment 2 of thepresent invention;

FIG. 8 is a cross-sectional view showing the conventional type ofcurvature variable reflecting curved-face mirror; and

FIG. 9 is a perspective view showing the conventional type of curvaturevariable reflecting curved-face mirror.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description is made hereinafter for Embodiment 1 according to thepresent invention with reference to FIG. 1, FIG. 2, FIG. 4, FIG. 5, FIG.6, and FIG. 7. It should be noted that, FIG. 1 is a diagram showingconfiguration of an optical path, a holder for curvature variablereflector and a key section of the piping system of the laser machiningapparatus according to Embodiment 1 of the present invention, and FIG. 2is a diagram showing another embodiment of the configuration of opticalpath and key section of the piping system of the laser machiningapparatus according to Embodiment 1 of the present invention.

Also FIG. 3 is a diagram showing the piping system and its constructionin a case where air 15 discharged from the holder 9 for curvaturevariable reflector of the laser machining apparatus according toEmbodiment of the present invention, FIG. 4 is a diagram showing acontrol circuit for keeping a diameter of the laser beam at a constantvalue at a position of the machining lens 29, FIG. 5 is a diagramshowing a control circuit for moving the machining head 28 in theZ-axial direction corresponding to a change of a distance from themachining lens 29 to the minimum converging spot diameter, and FIG. 6 isa diagram showing an alarm circuit for a pressure of air 15 supplied tothe holder 9 for curvature variable reflector.

In FIG. 1, designated at the reference numeral 9 is a holder for acurvature variable reflector, at 10 a curvature variable reflector whichis a laser beam reflecting member capable of varying the curvatureaccording to a fluid pressure such as air, at 11 a circular supportingplate which is a key section of the reflecting member supporting sectionsupporting the peripheral portion of the curvature variable reflector10, at 12 a holding plate for fixing the peripheral portion of thecurvature variable reflector 10, at 13 an air jacket, at 14 an air inletport provided in the central section of the air jacket 13, at 15 air, at16 air paths provided at several positions at an even space from eachother on the circular supporting plate 11, at 17 an air path provided inthe air jacket 13 and formed on the peripheral section of the circularsupporting plate 10, at 18 an air outlet port, at 19 a pressure gauge,at 20 a laser beam outputted from a laser oscillator not shown herein,at 21 a laser beam reflecting surface of the curvature variablereflector 10, at 22 a laser beam non-reflecting surface (a rear surface) of the curvature variable reflector 10, at 23 a fixing screw, at 24ato 24d O-rings each for keeping hermeticity thereof, at 25a, 25b, and25c electromagnetic valves each for turning air ON/OFF, at 26a, 26b, and26c regulators each for setting an air pressure, at 27a and 27breflectors each for reflecting the laser beam 20, at 28 a machininghead, at 29 a machining lens which is a converging optical membersupported with the machining head 28, at 30 a machining lens retainerfor retaining the machining lens 29, at 31 an inlet port for machininggas, at 32 gas for machining, at 24e an O-ring for sealing the gas 32for machining, at 33 a work irradiated with laser beam 20 focused, andat 34 a control unit.

Also in FIG. 2, the reference numeral 35 indicates an electropneumaticvalve for enabling variation of supplying air pressure smoothly.

Also in FIG. 3, designated at the reference numeral 50 is a flowcontroller for controlling a constant flow rate irrespective of pressuredue to supplied fluid, at 51 a supply port for purge air, at 52 a laserbeam transfer path, at 53 a cover made with rubber for dustproofing andsealing, and at 54 an air flow.

Also in FIG. 4, the reference numeral 55 indicates a curvature computingunit for computing a curvature of the curvature variable reflector 10required for a certain specified laser beam diameter at a position ofthe machining lens 29. Also in FIG. 5, the reference numeral 56indicates a computing unit for a distance to a minimum converging spotdiameter for computing a distance from the machining lens 29 to theminimum converging spot diameter, and the numeral 57 indicates a lasermachining apparatus, and also in FIG. 6, the numeral 58 indicates acomparator, and the numeral 59 indicates an alarm unit.

Next, a description is made for operations. In the curvature variablereflector 10 made from a material elastically deformable due to a fluidpressure, the peripheral portion thereof is supported by the circularsupporting plate 11, and also pressed to the circular supporting plate11 with the holding plate 12 fixed with the fixing screws 23 to the airjacket 13. On the other hand, in the air jacket 13, air 15 is suppliedthrough the air inlet port 14 provided in the central section thereof byopening any of the electromagnetic valves 25a, 25b, and 25c. Each of theregulators 26a, 26b, and 26c are installed right behind theelectromagnetic valves 25a, 25b, and 25c respectively, a pressure can beswitched to three stages by presetting each of the regulators. And theswitching is executed according to an instruction from the control unit3 for controlling the entire laser machining apparatus.

In laser machining such as cutting and welding, a diameter of a laserbeam coming into a converging optical member such as a machining lens 29is one of the extremely important factors because it substantiallydecides a minimum converging spot diameter, and there is an optimallaser beam diameter to each work according to a type (quality) or athickness of the work 33. For this reason, better quality lasermachining can be executed in stable conditions by changing the diameterof a laser beam coming into a converging optical member according to atype or thickness of the work 33.

Then, as for the air 15 supplied from the air inlet port 14, a fluidoperating circuit is constructed so that the air passes through theseveral air paths 16 each provided equally spaced to each other on thecircular supporting plate 11, and goes out to the air paths 17 providedin the peripheral section of the circular supporting plate 11, and thenis discharged from the air outlet port 18 provided on one place of theair jacket 13, and this fluid pressure deforms a shape of the curvaturevariable reflector 10 to a spherical one, so that it can be used as aspherical mirror (in this case, a convex mirror). It should be notedthat the internal diameter of the air outlet port 18 is made smaller ascompared to the internal diameter of the air inlet port 14, so that apressure can be added to the laser beam non-reflecting surface (a rearsurface) of the curvature variable reflector 10 with a small quantity offlow rate. And also the curvature thereof can be switched to threestages according to an instruction from the control unit 34 because acurvature of the curvature variable reflector 10 is changed inassociation with a change of a fluid pressure. Also a curvature of thecurvature variable reflector 10 can be changed at almost the same timewhen an instruction is outputted from the control unit 34 according to afluid pressure in association with a supply rate of the fluid suppliedto the fluid operating circuit. It should be noted that O-rings 24a,24b, 24c, and 24d are used for keeping hermeticity thereof.

On the other hand, when the shape of the curvature variable reflector 10is deformed to a spherical one, astigmatism is generated because ofreflection, the laser beam 20 emitted from the laser oscillator (notshown herein) is introduced into the curvature variable reflector 10making an incidence angle thereof as small as possible, and istransferred to the machining head 28 by the reflectors 27a and 27b. Thenthe laser beam is focused through the machining lens 29, and irradiatedonto a work 33 near the focused position, and in this step, according toan instruction from the control unit 34, the machining head 28 or thework 33 moves and machining gas 32 supplied from the machining gas inletport 31 is injected to the same axis as that of focused laser beam 20,so that machining such as cutting or welding can be executed. It shouldbe noted that the O-ring 24e is used for sealing the machining gas 32,and a machining lens retainer 30 is used for retaining the machininglens 29.

As shown in FIG. 2, a pressure of the supplied air 15 can smoothly bechanged because an electropneumatic valve 35 is used. For this reason, acurvature of the curvature variable reflector 10 can be changedsmoothly, in other words continuously according to an instruction fromthe control unit 34.

Also in the laser beam transfer path, air purging is executed quiteoften to prevent dust or a poisonous gas from coming thereinto and tokeep a stability of the laser beam, but in the configuration accordingto the present invention where air discharged from the air outlet port18 is again supplied to inside of the laser beam transfer path, a purgeair supply unit comprising a compressor, a drier, and a filer or thelike which has been specially prepared for executing purging based onthe conventional technology is not required.

As a concrete system thereof, as shown in FIG. 3, a flow rate of the air15 discharged from the air outlet port 18 is kept constant by the flowcontroller 50 (a flow rate control valve), and the air is continuouslysupplied to the laser beam transfer path 52 through the purge air supplyport 51 to keep an atmosphere in the laser beam transfer path 52 at aconstant level.

When a light scan type of laser machining apparatus in which themachining head 28 moves on an X-Y plane and executes machining is used,conventionally it is impossible to keep constant a diameter of a laserbeam coming into the machining lens 29 even if a collimation is used,but with the control unit 34, it is possible to keep a diameter of alaser beam coming into the machining lens 29 at a constant value bycontinuously changing a curvature of the curvature variable reflector 10in association with movement of the machining head 28 in the X-Ydirection.

As a concrete system thereof, as shown in FIG. 4, a beam transferdistance from the laser oscillator (not shown herein) to the machininglens 29 is computed by the control unit 34, and according to thecomputed transfer distance, a curvature of the curvature variablereflector 10 required for a decided laser beam diameter is computed bythe curvature computing unit 55 at the position of the machining lens29. Then, an instruction is given to the electropneumatic valve 35 for asupply air pressure to the holder 9 for the curvature variable reflectorcorresponding to one of the curvatures previously computed and inputtedinto the control unit 34. In a case where the curvature computing unit55 is not used, it is advised to previously prepare data for curvaturesrequired for deciding a laser beam diameter like in a case of the supplyair pressure to the holder 9 of curvature variable reflector and storethe data in the control unit 34.

When a diameter of a laser beam coming into the machining lens 29 ischanged, a distance from the machining lens 29 to the minimum convergingspot diameter slightly changes. Also in a case where a light scan typeof laser machining is executed, a minimum converging spot diameter canbe kept nearly constant by keeping a laser beam diameter constant evenif the machining head 28 is moved. However, because a distance to theminimum converging spot diameter is likely changed, it is possible tocontrol movement of the machining head 28 or machining lens 29 in theZ-axial direction so that a position of a minimum converging spotdiameter in the Z-axial direction (upward or downward) will be keptconstant.

As a concrete system, as shown in FIG. 5, in addition to the curvaturecomputing unit 55, a computing unit 56 for computing a distance to aminimum converging spot diameter is added thereto, and the distance fromthe machining lens 29 to the minimum converging spot diameter iscomputed, and then the control unit 34 outputs an instruction to thelaser machining apparatus 57 to move the machining head 28 in theZ-axial direction so that the distance thereof will be equal to thecomputed one.

Also a plurality of curvature variable reflectors 10 and the holder 9thereof each are installed in the laser beam transfer paths, so that avariable range of the laser beam diameter can be expanded.

Also a pressure of the air 15 supplied to the holder 9 for curvaturevariable reflector is monitored, and when a difference equal to orlarger than a prespecified value is generated between the monitoredfluid pressure and an instructed pressure value by the control unit 34,the state is regarded as an abnormal one, and an alarm is generated oroperation of the laser machining apparatus is stopped.

As a concrete system, as shown in FIG. 6, a pressure instruction valueoutputted from the control unit 34 to the electropneumatic valve 35 iscompared to a fluid pressure actually supplied to the holder 9 forcurvature variable reflector with a comparator 58, and if the value ofthe difference is larger than the preset one, the instruction istransferred to the alarm unit 59 to issue an alarm alerting the state.

Also there has been employed an approach for registering machiningconditions such as a machining speed, a machining output, and amachining gas pressure in the control unit 34 according to a quality ora thickness of a work 33, but there is an optimal laser beam diametermost suited to particular quality or thickness of the work 33, so thatthe laser beam diameter is added anew to the registered items ofmachining conditions (the laser beam diameter to be registered should beselected from various types of laser beam diameters previouslyprepared). Then with the approach described above (in which thecurvature computing unit 55 is used or data for laser beam diameters isprepared previously), it is possible to control the beam diameter at aposition of machining lens 29 so that it will always be one of thoseregistered in registration of machining conditions even if the machininghead 28 moves.

In Embodiment 1, a case was described where the curvature variablereflector 10 be deformed to a spherical one, but if a construction ofthe holder and that of a piping system of the laser machining apparatusare made as shown in FIG. 7, an air is supplied from the air inlet port43a and at the same time the electromagnetic valves 25d and 25e areclosed, a fluid can be supplied to a space defined by the piston 41 andthe cylinder (1) 40 and the piston 41 moves in the direction of thearrow in the figure sliding along the cylinder (1) 40 and the cylinder(2) 42, and thereby a pressure is loaded to the side of the laser beamnon-reflecting surface (a rear surface), so that a shape of thecurvature variable reflectors 10 can be changed to that of a concavemirror. It should be noted that the shape can be changed to that of aconvex mirror as in Embodiment 1 by opening the electromagnetic valves25d and 25e and supplying an air thereto from the air inlet port 43b.For this reason with the construction as described above, it becomespossible to use the curvature variable reflector as either a concavemirror or a convex mirror, so that a variable range of a laser beamdiameter can be expanded.

In Embodiment 1, the curvature variable reflector 10 is a plane mirrorin a state where a pressure is not loaded thereto, but the mirror may beeither a concave mirror or a convex one.

Also in Embodiment 1, a wall thickness of the plane mirror is even, butthe wall thickness may be changed according to a distance from thecenter of the plane mirror to the peripheral section to obtain an idealspherical curvature.

Also in Embodiment 1, air is employed as a fluid for loading a pressure,but it may not necessarily be air, and other type of gas may be used forit. Also it may not necessarily be a gas, and a liquid such as water maybe used for it.

Also in FIG. 1, a number of units of electromagnetic valves are three,and a pressure thereof is switched in three stages, but they are notnecessarily to be three, and there is not specific restriction over thenumber of electromagnetic valves nor over the number of switchingstages. It should be noted that if many electromagnetic valves are used,also many laser beam diameters are available, which insures better andmore stable laser machining can be executed.

Also in Embodiment 1, air for loading a pressure is used also forpurging, but the air may be used as a machining gas required for lasermachining.

As described above, with the present invention, the laser machiningapparatus comprises a laser beam reflecting member which elasticallydeforms according to a fluid pressure provided in a transfer path forthe laser beam, a reflecting member supporting section for supporting aperipheral section of this laser beam reflecting member and alsodefining a space in a side opposite to a laser beam reflecting surfacetogether with the laser beam reflecting member, a fluid supplying meansfor supplying a fluid into the space defined by this reflecting membersupporting section, and a fluid discharging means for discharging afluid from the space defined by the reflecting member supportingsection, and the space is sealed excluding a fluid feed path and a fluiddischarge path thereof, a fluid path in which a fluid supplied into thespace is discharged to outside thereof is defined by contacting with alaser beam reflecting surface, and a fluid pressure required for thelaser beam reflecting member to elastically deform is loaded to thelaser beam reflecting surface, so that a laser beam diameter can becontrolled at high velocity as required by quickly changing curvature ofthe laser beam reflecting member, and at the same time the laser beamreflecting member is cooled due to a supplied fluid, and heatdeformation of a laser beam reflecting member due to irradiation with alaser beam is prevented.

Also the apparatus comprises a fluid pressure control means, and cancontinuously change curvature of the laser beam reflecting member due toits elastic deformation and can continuously control a diameter of alaser beam coming into a converging optical member by continuouslycontrolling a supplied fluid pressure.

Also after the fluid supplied to elastically deform the laser beamreflecting member is discharged from the fluid discharge means, thefluid is supplied into the laser beam transfer path, and is used forpurging inside of the laser beam transfer path as a purge air, so thatconfiguration of a laser beam machining apparatus can be simplified andalso running costs thereof can be reduced.

Also, the apparatus comprises a means for controlling curvature of thelaser beam reflecting member so that, when a light scan type of lasermachining in which a machining head moves on an X-Y plane and executesmachining is executed, a diameter of a laser beam coming into theconverging optical member mounted on the machining head will be keptconstant irrespective of a position of the machining head, so thatquality laser machining can be executed at its steady level.

Also, the apparatus comprises a means for controlling a basic body ofthe machining head or the converging optical member mounted on themachining head to move in the Z-axial direction so that a position ofthe minimum converging spot diameter in the Z-axial direction will bekept constant, so that quality laser machining can be executed at asteady level.

Also, a plurality of laser beam reflecting members which elasticallydeform due to a fluid pressure are provided in the laser beam transferpath, so that a variable range for a laser beam diameter can beexpanded.

Also, a supplied fluid pressure is monitored when a pressure of a fluidsupplied into the space defined by the reflecting member supportingsection is being controlled and alarm can be generated or operation canbe stopped when a difference equal to or larger than a prespecifiedvalue is generated between the monitored fluid pressure and aninstructed pressure value.

Also, optimal laser beam diameters each are previously registered as oneof machining conditions and one of the laser beam diameter is selectedaccording to a quality or a plate thickness of a work, so that qualitylaser machining can be executed at its steady level.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A laser machining apparatus for machining a workby focusing thereon a laser beam emitted from a laser oscillator along alaser beam transfer path, said apparatus comprising:a laser beamreflecting member having an elastically deformable laser beam reflectingsurface, an opposite surface, and a peripheral section; a reflectingmember supporting section supporting said peripheral section and,together with said opposite surface of said laser beam reflectingmember, defining a space; means for supplying a fluid into said spacealong a fluid feed path; and means for discharging said fluid from saidspace along a fluid discharge path;wherein said space, except for saidfluid feed path and said fluid discharge path, is sealed; and whereinsaid laser beam reflecting surface elastically deforms according to afluid pressure exerted thereon by said fluid in said space, therebyproviding a reflecting surface curvature, said laser beam beingreflected by said laser beam reflecting surface according to saidreflecting surface curvature; wherein said laser machining apparatusfurther comprises a cover disposed around at least a part of said laserbeam transfer path and having a supply port, and means for providingfluid output from said fluid discharge path to said supply port; whereinsaid fluid purges the inside of said laser beam transfer path covered bysaid cover.
 2. A laser machining apparatus according to claim 1, furthercomprising:a machining head with a basic body, a converging opticalmember being mounted on said machining head; and means for keepingconstant, in a Z-axial direction, a minimum converging spot diameter ofsaid laser beam by controlling one of said basic body and saidconverging optical member to move in said Z-axial direction.
 3. A lasermachining apparatus for machining a work by focusing thereon a laserbeam emitted from a laser oscillator along a laser beam transfer path,said apparatus comprising:a laser beam reflecting member having anelastically deformable laser beam reflecting surface, an oppositesurface, and a peripheral section; a reflecting member supportingsection supporting said peripheral section and, together with saidopposite surface of said laser beam reflecting member, defining a space;means for supplying a fluid into said space along a fluid feed path; andmeans for discharging said fluid from said space along a fluid dischargepath;wherein said space, except for said fluid feed path and said fluiddischarge path, is sealed; and wherein said laser beam reflectingsurface elastically deforms according to a fluid pressure exertedthereon by said fluid in said space, thereby providing a reflectingsurface curvature, said laser beam being reflected by said laser beamreflecting surface according to said reflecting surface curvature;wherein said laser machining apparatus further comprises means formonitoring a supplied fluid pressure and generating an alarm or stoppingsaid machining when a difference between the monitored fluid pressureand an instructed pressure value reaches a prespecified threshold.
 4. Alaser machining apparatus for machining a work by focusing thereon alaser beam emitted from a laser oscillator along a laser beam transferpath, said apparatus comprising:a laser beam reflecting member having anelastically deformable laser beam reflecting surface, an oppositesurface, and a peripheral section; a reflecting member supportingsection supporting said peripheral section and, together with saidopposite surface of said laser beam reflecting member, defining a space;means for supplying a fluid into said space along a fluid feed path;means for discharging said fluid from said space along a fluid dischargepath; a cover disposed around at least a part of said laser beamtransfer path and having a supply port, and means for providing fluidoutput from said fluid discharge path to said supply port;wherein saidspace, except for said fluid feed path and said fluid discharge path, issealed; wherein said laser beam reflecting surface elastically deformsaccording to a fluid pressure exerted thereon by said fluid in saidspace, thereby providing a reflecting surface curvature, said laser beambeing reflected by said laser beam reflecting surface according to saidreflecting surface curvature; wherein said fluid supplying meanscontinuously supplies said fluid during said machining; wherein saidlaser machining apparatus further comprises a fluid pressure controlmeans for continuously controlling said fluid pressure of said fluid insaid space so as continuously to control said reflecting surfacecurvature; and wherein said fluid purges the inside of said laser beamtransfer path covered by said cover.
 5. A laser machining apparatusaccording to claim 4, wherein said laser beam transfer path includesmore than one said laser beam reflecting member.
 6. A laser machiningapparatus according to claim 4, further comprising:a machining head witha basic body, a converging optical member being mounted on saidmachining head; and a control unit for controlling said fluid pressurecontrol means;wherein said machining head executes said machining whilemoving on an X-Y plane; and wherein said control unit controls saidfluid pressure control means so that a diameter of said laser beamcoming into said converging optical member is kept constant irrespectiveof a position of said machining head.
 7. A laser machining apparatusaccording to claim 6, wherein said laser beam transfer path includesmore than one said laser beam reflecting member.
 8. A laser machiningapparatus according to claim 6, wherein a plurality of optimal laserbeam diameters are previously registered, each defining a machiningcondition, and one of said plurality of laser beam diameters is selectedaccording to at least one of a quality and a plate thickness of saidwork.
 9. A laser machining apparatus according to claim 6, furthercomprising:means for keeping constant, in a Z-axial direction, a minimumconverging spot diameter of said laser beam by controlling one of saidbasic body and said converging optical member to move in said Z-axialdirection.
 10. A laser machining apparatus for machining a work byfocusing thereon a laser beam emitted from a laser oscillator along alaser beam transfer path, said apparatus comprising:a laser beamreflecting member having an elastically deformable laser beam reflectingsurface, an opposite surface, and a peripheral section; a reflectingmember supporting section supporting said peripheral section and,together with said opposite surface of said laser beam reflectingmember, defining a space; means for supplying a fluid into said spacealong a fluid feed path; and means for discharging said fluid from saidspace along a fluid discharge path;wherein said space, except for saidfluid feed path and said fluid discharge path, is sealed; wherein saidlaser beam reflecting surface elastically deforms according to a fluidpressure exerted thereon by said fluid in said space, thereby providinga reflecting surface curvature, said laser beam being reflected by saidlaser beam reflecting surface according to said reflecting surfacecurvature; wherein said fluid supplying means continuously supplies saidfluid during said machining; wherein said laser machining apparatusfurther comprises a fluid pressure control means for continuouslycontrolling said fluid pressure of said fluid in said space so ascontinuously to control said reflecting surface curvature; wherein saidreflecting member supporting section comprises a circular supportingplate disposed in an air jacket; wherein said fluid discharge pathcomprises a plurality of equally spaced air paths, formed in saidcircular supporting plate, communicating with said space; and whereinsaid fluid discharge path further comprises an annular air path of saidair jacket, each of said plurality of equally spaced air pathscommunicating with said annular air path, said annular air pathcommunicating with an air outlet port.
 11. A laser machining apparatusaccording to claim 10, wherein said air outlet port has an innerdiameter that is smaller than an inner diameter of said fluid feed path.12. A laser machining apparatus for machining a work by focusing thereona laser beam emitted from a laser oscillator along a laser beam transferpath, said apparatus comprising:a laser beam reflecting member having anelastically deformable laser beam reflecting surface, an oppositesurface, and a peripheral section; a reflecting member supportingsection supporting said peripheral section and comprising a cylindersection and a piston section in slideable contact therewith, there beinga first space between said opposite surface of said laser beamreflecting member and a surface of said piston, there being a secondspace between said piston section and said cylinder section, said firstspace having a respective volume based on a position of said pistonsection within said cylinder section; means for supplying fluid intosaid first and second spaces, respectively, along first and second fluidfeed paths; means for discharging said fluid from said first and secondspaces, respectively, along first and second fluid discharge paths; saidspaces, except for said fluid feed paths and said fluid discharge paths,being sealed; said laser beam reflecting surface elastically deformingaccording to a first fluid pressure exerted thereon by said fluid insaid first space to provide a reflecting surface curvature, said laserbeam being reflected by said laser beam reflecting surface according tosaid reflecting surface curvature; and said position of said pistonbeing determined according to a second fluid pressure of said fluid insaid second space.